Why are there dark streaks on my roof?

Have you ever looked up at your roof or another roof in your neighborhood and noticed dark streaks forming? Those streaks didn’t happen overnight. But there is a good chance you didn’t notice them until they really became an eyesore. So why are there dark streaks on your roof?

What are the dark spots forming on your roof?

Those dark spots may not be what you think. It isn’t dirt and it isn’t the result of anything falling off of your trees. It’s actually a type of roof algae. In technical terms, it is Gloeocapsa Magma. It can happen on any asphalt roof but you’ll probably notice it first on your shingles that face west or north. You also may notice it on other homes in your neighborhood before it develops on yours. But once it hits a neighborhood, most homes with asphalt roofs will eventually notice the algae forming.

Why does algae form on the roof?

The reason the algae forms on roofs is the result of a combination of factors. One of those reasons is because asphalt shingles contain limestone dust. Algae thrives on lime-based products making your shingles a perfect target. It is an airborne algae so it is going to travel through the air via normal wind blowing, making it difficult to prevent. That, in combination with humidity and warm weather, has allowed the algae to spread further north. The dark spots that you see are a result of a dark pigment that shields the algae from ultraviolet rays from the sun.

What should I do if I notice streaks on my roof?

If you are noticing these dark streaks on your roof, there is no need to panic. Although it may look like your roof is leaking or retaining water, this isn’t the case. The algae is also not something that is going to negatively impact the integrity of your roof. All you really need to do is get in the habit of some basic roof maintenance, including keeping your roof clean. When cleaning your roof, it is important that you never use a pressure washer. Doing so could damage your shingles, possibly damage their protective coating, and in some cases void your roof’s warranty. But you can get up there and spray your roof with a pump operated garden sprayer using a mixture of 1 cup trisodium phosphate, 1 gallon of bleach, and 5 gallons of water. Allow the solution to sit for 20 minutes and then rinse.

If you have any questions about the streaks on your roof, or any other roofing related questions, contact our local roofing experts. If needed, we’ll come out to inspect the roof of your home and outline your options. Contact us using the form or give us a call at 414-332-1139.

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